The present invention is directed to a package assembly containing a hydrogen getter and to an electrical enclosure containing a hydrogen getter package assembly. More particularly, the invention is directed to a hydrogen getter package assembly for removing hydrogen from a large volume electrical enclosure and protecting electrical assemblies, and subassemblies of components from hydrogen degradation.
Many microelectronic devices such as semiconductors are known to be degraded by exposure to hydrogen. Hydrogen degradation is particularly a problem with certain electronic devices such as pseudomorphic high electron mobility transistors (PHEMT) of monolithic millimeter wave integrated circuits (MMIC). These devices include thin silicon nitride (Si3N4) passivation layers that provide the sensitive channel little protection from hydrogen degradation. Therefore, very low concentrations of hydrogen in environmentally sealed electrical enclosures can result in hydrogen degradation of the electrical components thereby shortening the useful life of the components.
Hydrogen can be released from various sources within an enclosure containing electronic assemblies and subassemblies. Hydrogen does not readily escape from environmentally sealed enclosures and reacts with the hydrogen sensitive components. Certain metals and nonmetals used to produce the electronic components can contain dissolved hydrogen that is released over time. The package materials such as some plastic materials can also release hydrogen. For example, plated nickel layers used as a barrier layer for gold plating operations and plastic resins are known to release hydrogen in amounts that can degrade the electrical components contained in the sealed enclosure.
Various processes have been proposed in the past to reduce the amount of hydrogen in the enclosure. One effort has been to heat the materials and particularly the housing materials to drive hydrogen and other gases from the materials prior to assembling the enclosure. This method has been successful in some instances where enclosure materials can be effectively depleted of hydrogen or the amount of hydrogen remaining is reduced to a sufficiently low level to minimize hydrogen degradation of the electrical components. This method is only suitable for materials that can be heated to very high temperatures, typically 250xc2x0 C. and above, without degrading the materials.
The degradation of the electrical component assemblies and subassemblies by hydrogen is not completely understood. The generally accepted explanation is that the platinum group metals function as catalysts for the dissociation of molecular hydrogen to atomic hydrogen. The atomic hydrogen is then able to diffuse into the other areas of the electrical device. It is believed that atomic hydrogen in GaAs transistors diffuses directly into the channel area where it neutralizes the silicon donors or diffuses into the metal, such as titanium, that swells and imposes piezo resistance stresses on the channel.
Another method of controlling the hydrogen concentration in an electrical device is to include a hydrogen scavenger in the package. Hydrogen scavengers are generally referred to in the art as hydrogen getters. Many hydrogen getters require a vacuum or an inert atmosphere.
One form of hydrogen getter uses an alloy of metals such as iron, nickel, titanium, vanadium, zirconium, chromium, cobalt, rare earth metals and other metals that react with hydrogen to form metal hydrides. These hydrogen getters generally require temperatures of over 300xc2x0 C. to function effectively. The metals are also poisoned by oxygen, water vapor, chlorine and other contaminants. Therefore, this type of hydrogen getter is limited to environments that are able to maintain a sufficient operating temperature. Since many electrical components cannot withstand these temperatures, these systems are generally not useful for electrical enclosures.
Another type of hydrogen getter includes a platinum group metal such as palladium formed on a substrate. One example of a common substrate is activated carbon. The platinum group metal is applied as a mixture of the metal and an unsaturated organic compound, such as diphenyl butadiene or 1,4-bis(phenylethylene)benzene. The platinum group metal functions as a catalyst in the mixture to bind the hydrogen to the functional groups of the organic molecule. These devices operate at moderate temperatures and are not poisoned by oxygen or water vapor. However, a disadvantage of this type of device is the vapor pressure and melting point of the organic component.
Other devices have been proposed to overcome the disadvantages of the prior devices. One example forms a hydrogen getter from a mixture of a platinum group metal, a desiccant, and a gas permeable binder. The binder is cured in a gas with effective amounts of oxygen at a temperature to stabilize the mixture from self-catalytic degradation. An example of this type of hydrogen getter is disclosed in U.S. Pat. No. 5,888,925 to Smith et al.
Another example of a hydrogen getter is disclosed in U.S. Pat. No. 4,014,346 to Brownlee et al. This device discloses a cardiac pacemaker including a hydrogen getter. The hydrogen getter is a palladium sponge or lanthanum pentanickel. The devices have the disadvantage of having a low hydrogen adsorption capacity compared to the volume of the getter. Therefore, these devices are limited to small volume enclosures and devices.
Still another type of hydrogen getter uses a zeolite where at least a portion of the sodium has been replaced with an activated metal. For example, U.S. Pat. No. 3,108,706 to Matsch et al. relates to a vacuum insulator for storing low boiling liquefied gases. The vacuum chamber includes a silver exchanged zeolite. U.S. Pat. No. 4,717,236 to Dewing discloses an optical fiber cable. The cable is filled with a water blocking compound and a zeolite having some of the sodium replaced by silver.
U.S. Pat. No. 6,110,808 to Saito discloses a microelectronic assembly including a hermetically sealed package. The package includes a housing, a base layer bonded to the housing, an intermediate layer of hydrogen absorbing metal, a top layer of metal able to convert molecular hydrogen to atomic hydrogen and is able to absorb hydrogen.
While the above-noted devices have been generally effective for the intended purpose, these devices are not suitable for many environments. The prior devices relating to electronic assemblies utilize expensive rare earth metals and require at least 10 times the surface area compared to other hydrogen getters. In addition, some of these devices require being sealed in a hermetic enclosure to 10xe2x88x927 cc/sec (He). Accordingly, there is a continuing need in the industry for improved devices for absorbing and removing hydrogen from an electrical enclosure containing electrical assemblies and subassemblies.
The present invention is directed to a package assembly for a hydrogen getter. More particularly, the invention is directed to a hydrogen getter package assembly for removing hydrogen from a large volume electrical enclosure and protecting electrical assemblies and subassemblies from hydrogen degradation. The hydrogen getter package is effective in scavenging hydrogen from electrical enclosures having an internal volume of 10s of liters.
Accordingly, a primary aspect of the invention is to provide a package containing a hydrogen getter where the package is made from a hydrogen permeable and moisture impermeable material.
Another aspect of the invention is to provide a package containing an activated metal-ion exchanged zeolite as a hydrogen getter.
A further aspect of the invention is to provide a hydrogen getter package made from a hydrogen permeable, moisture impermeable inner layer and a hydrogen and moisture permeable outer layer.
Another aspect of the invention is to provide a package for a hydrogen getter where the package includes an inner layer of a polyethylene film and an outer layer of a spun bonded polyethylene.
Still another aspect of the invention is to provide a hydrogen getter package having an internal wall forming a first compartment containing a hydrogen getter and a second compartment containing a desiccant. In one embodiment, the compartment containing the hydrogen getter can be evacuated and sealed such that the ambient air and moisture within the cavity is removed so as not to poison the hydrogen getter.
A further aspect of the invention is to provide a hydrogen getter package assembly having a thermal insulating internal wall forming a first compartment containing a hydrogen getter and a second compartment containing a desiccant.
The aspects of the invention are basically attained by providing a package assembly containing a hydrogen getter. The package assembly includes a container, such as a flexible pouch or envelope forming an enclosed cavity. The package includes at least one wall made from a hydrogen permeable and moisture impermeable material.
The aspects of the invention are also attained by providing a hydrogen getter package assembly comprising a package enclosing a hydrogen getter. The package includes a first wall that is permeable to hydrogen and moisture and a second wall that is permeable to hydrogen and impermeable to moisture. The package can include an inner wall forming a first compartment containing the hydrogen getter and a second compartment containing a desiccant.
The aspects of the invention are further attained by a package assembly for a hydrogen getter where the assembly includes a first container made from a hydrogen permeable and moisture impermeable material enclosing a hydrogen getter and a second container enclosing the first container and containing a desiccant. The second container is made from a hydrogen permeable and moisture permeable material.
The various aspects of the invention are further attained by providing an electrical housing for enclosing an electrical component such as a GaAs FET, GaAs MMIC or GaAs HBT electrical device. The housing includes a hydrogen getter assembly that includes a package containing a hydrogen getter. The package includes an inner compartment made from a hydrogen permeable and moisture permeable material, which contains the hydrogen getter. The inner compartment is enclosed within an outer compartment containing a desiccant for adsorbing moisture from the inner compartment. The outer compartment is made from a hydrogen permeable and moisture impermeable material. The hydrogen getter assembly can be placed against the electrical component with the electrical component acting as a heat source to drive moisture from the inner compartment to the adsorbent in the outer compartment.
These and other aspects, advantages and salient features of the invention will become apparent to those skilled in the art in view of the annexed drawings and the following detailed description of the invention.